Method for enhanced split injection in internal combustion engines

ABSTRACT

A method for controlling a compression-ignition internal combustion engine which provides delivery of multiple fuel injection pulses per cylinder firing with precision of pulse quantities, separation, and timing adequate for transition between split and single injection at any speed and load, without disturbing the primary engine governor. The method compensates for variable operating conditions such as supply voltage, injection pressure, injection pulse separation, and injector actuation latency or rise-time.

This is a continuation of copending application Ser. No. 08/870,781,filed on Jun. 6, 1997.

TECHNICAL FIELD

The present invention relates to a method for controlling acompression-ignition internal combustion engine.

BACKGROUND ART

In the control of fuel injection systems, the conventional practiceutilizes electronic control units having volatile and non-volatilememory, input and output driver circuitry, and a processor capable ofexecuting a stored instruction set, to control the various functions ofthe engine and its associated systems. A particular electronic controlunit communicates with numerous sensors, actuators, and other electroniccontrol units necessary to control various functions, which may includevarious aspects of fuel delivery, transmission control, or many others.

Fuel injectors utilizing electronic control valves for controlling fuelinjection have become widespread. This is due to the precise controlover the injection event provided by electronic control valves. Inoperation, the electronic control unit determines an energizing orexcitation time for the control valve corresponding to current engineconditions. The excitation of the control valve causes a cascade ofhydraulic events leading to the lifting of the spray tip needle, whichcauses fuel injection to occur.

Several attempts have been made to enhance fuel injection capabilities.One such method is known as split injection. Split injection consists ofa first injection, called the pilot injection, followed by a delay, andthen a second injection, referred to as the main injection. Whenperforming split injection, precise control over pulse quantities,timing, and separation is essential. Many times, operating conditions atwhich split injection may be performed are restricted to lower enginespeeds due to difficulties in achieving precise control over theinjection process.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a systemand method for enhanced split injection which allows for smoothtransition between split injection and single injection at any enginespeed and load, without disturbing the primary engine governor.

It is an object of the present invention to provide an improved systemand method for controlling fuel delivery in a fuel injector having anelectronic control valve.

It is another object of the present invention to provide a system andmethod for accurately determining control valve rise-time.

It is another object of the present invention to provide a system andmethod for improved pulse width determination.

It is another object of the present invention to eliminate systematicinfluences which would otherwise detract from fuel delivery accuracy.

In carrying out the above objects and other objects and features of thepresent invention, a system and method for controlling fuel delivery ina fuel injector having an electronic control valve is provided. Themethod comprises establishing pilot and main injection rise-times forthe control valve. Pilot excitation time is determined based on thepilot injection rise-time and a pilot fuel quantity. A desiredinter-pulse gap between a pilot injection termination and a maininjection actuation is determined. The desired inter-pulse gap ispreferably based on engine RPM and varies so as to permit splitinjection at a wide range of engine speeds and loads. Main excitationtime is determined based on the inter-pulse gap, main injectionrise-time, and a main fuel quantity.

In a preferred embodiment, the method comprises the step of measuringavailable battery voltage. The main injection rise-time is further basedon the inter-pulse gap and the available battery voltage.

The advantages accruing to the present invention are numerous. Forexample, the method of the present invention provides delivery ofmultiple fuel injection pulses per cylinder firing with precision ofpulse quantities, separation, and timing adequate for transition betweensplit and single injection at any speed and load, without disturbing theprimary engine governor. The method compensates for variable operatingconditions such as supply voltage, injection pressure, injection pulseseparation, and injector actuation latency or rise-time.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fuel injection system made inaccordance with the present invention;

FIG. 2 is a functional block diagram illustrating fuel delivery controlin accordance with the present invention;

FIG. 3 is a timing diagram illustrating fuel delivery control inaccordance with the present invention;

FIG. 4 is a block diagram illustrating a method of the present inventionfor controlling fuel delivery;

FIG. 5 is a block diagram illustrating a method of the present inventionfor determining filtered injector rise-time;

FIG. 6 is a block diagram illustrating a method of the present inventionfor pulse width direction adjustment to provide correct injectedquantity while there exists deviation between intended and actualinjection pressure;

FIG. 7 is a graph depicting a split main injection rise-time adjustmentfactor versus inter-pulse gap which compensates for the effect ofgradually diminishing solenoid magnetism on main rise-time;

FIG. 8 is a graph depicting another main injection rise-time adjustmentfactor versus available battery voltage for injectors in which theopening of the control valve initiates injection;

FIG. 9 is a graph depicting a valve actuation detection adjustmentfactor versus available battery voltage, and optionally injectionpressure;

FIG. 10 is a graph depicting a pulse width adjustment factor versus aninjection pressure ratio of observed pressure to desired pressure;

FIG. 11 is a graph depicting an injection delay factor versus availablebattery voltage which compensates for the influence of available batteryvoltage on control valve motion; and

FIG. 12 is a graph depicting a split main pulse width adjustment factorversus available battery voltage which significantly reduces theinfluence of available battery voltage on split main pulse quantityinjected.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, a system for enhanced split injection ininternal combustion engines is shown. The system, generally indicated byreference numeral 10, includes an engine 12 having a plurality ofcylinders, each fed by fuel injectors 14. In a preferred embodiment,engine 12 is a compression-ignition internal combustion engine, such asa four, six, eight, twelve, sixteen or twenty-four-cylinder dieselengine, or a diesel engine having any other desired number of cylinders.The fuel injectors 14 are shown receiving pressurized fuel from a supply16 which is connected to one or more high or low pressure pumps (notshown) as is well known in the art. Alternatively, embodiments of thepresent invention may employ a plurality of unit pumps (not shown), eachpump supplying fuel to one of the injectors 14.

The system 10 may also include various sensors 20 for generating signalsindicative of corresponding operational conditions or parameters ofengine 12, the vehicle transmission (not shown), and other vehicularcomponents. Sensors 20 are in electrical communication with a controller22 via input ports 24. Controller 22 preferably includes amicroprocessor 26 in communication with various computer readablestorage media 28 via data and control bus 30. Computer readable storagemedia 28 may include any of a number of known devices which function asa read-only memory (ROM) 32, random access memory (RAM) 34, keep-alivememory (KAM) 36, and the like. The computer readable storage media maybe implemented by any of a number of known physical devices capable ofstoring data representing instructions executable via a computer such ascontroller 22. Known devices may include, but are not limited to, PROM,EPROM, EEPROM, flash memory, and the like in addition to magnetic,optical, and combination media capable of temporary or permanent datastorage.

Computer readable storage media 28 include various program instructions,software, and control logic to effect control of various systems andsubsystems of the vehicle, such as engine 12, vehicle transmission, andthe like. Controller 22 receives signals from sensors 20 via input ports24 and generates output signals which may be provided to variousactuators and/or components via output ports 38. Signals may also beprovided to a display device 40 which includes various indicators suchas lights 42 to communicate information relative to system operation tothe operator of the vehicle.

A data, diagnostics, and programming interface 44 may also beselectively connected to controller 22 via a plug 46 to exchange variousinformation therebetween. Interface 44 may be used to change valueswithin the computer readable storage media 28, such as configurationsettings, calibration variables including adjustment factor look-uptables, control logic, and the like.

In operation, controller 22 receives signals from sensors 20 andexecutes control logic embedded in hardware and/or software to allowsmooth transitions between split injection and single injection at awide range of engine speeds and loads, without disturbing the primaryengine governor. In a preferred embodiment, controller 22 is the DDECcontroller available from Detroit Diesel Corporation, Detroit, Mich.Various other features of this controller are described in detail inU.S. Pat. Nos. 5,477,827 and 5,445,128, the disclosures of which arehereby incorporated by reference in their entirety. Additional featuresof the controller are described in detail in U.S. Pat. No. 5,839,420Issued on Nov. 24, 1998, entitled "System and Method of Compensating forInjector Variability", the disclosure of which is hereby incorporated byreference in its entirety.

With continuing reference to FIG. 1, a logic controller, such as logicunit 50, controls the signals sent to the fuel injectors 14. Logic unit50 determines rise-time adjustment factors, pulse width adjustmentfactors, pilot valve actuation detection delay adjustment factors,injection delay adjustment factors, and other injection parameters. Theadjustment factors and injection parameters are determined from variousengine operating conditions including but not limited to engine RPM,desired engine torque, available battery voltage, desired pilot to maininter-pulse gap, fuel temperature, measured fuel rail pressure (incommon rail systems), and desired fuel rail pressure (in common railsystems).

Further, logic unit 50 determines the type of injection required: splitor single, both of which may be smoothly switched between in accordancewith systems and methods of the present invention, as will be described.Logic unit 50 may be include in the functions of microprocessor 26, ormay be implemented in any other manner known in the art of hardware andsoftware control systems. It will be appreciated that logic unit 50 maybe a part of controller 22, or may be an independent control unit whichis in communication with controller 22.

As will be appreciated by one of ordinary skill in the art, the controllogic may be implemented or effected in hardware, software, or acombination of hardware and software. The various functions arepreferably effected by a programmed microprocessor, such as the DDECcontroller, but may include one or more functions implemented bydedicated electric, electronic, or integrated circuits. As will also beappreciated, the control logic may be implemented using any one of anumber of known programming and processing techniques or strategies andis not limited to the order or sequence illustrated here forconvenience. For example, interrupt or event driven processing istypically employed in real-time control applications, such as control ofa vehicle engine or transmission. Likewise, parallel processing ormulti-tasking systems and methods may be used to accomplish the objects,features, and advantages of the present invention. The present inventionis independent of the particular programming language, operating system,or processor used to implement the control logic illustrated.

Referring to FIG. 2, a functional block diagram illustrating enhancedsplit injection control is illustrated. Split injection, which is thedelivering of fuel in two discrete quantities can reduce nosie byreducing or eliminating ignition delay. A desired Engine GoverningTorque 58 is determined based on various operating conditions such asengine RPM, throttle position, and transmission gear ratio.Alternatively, fuel per cycle or percent load could be used for thepurposes of system control instead of Engine Governing Torque 58. LocalTorque or Final Torque 58 is divided into a Pilot Torque (PTQ) 60 and aMain Torque (MTQ) 62. The value of PTQ 60 is the lesser of the EngineGoverning Torque 58 and a Pilot Torque Limiting Value (EPIPTQ), notshown. The value of MTQ 62 is simply PTQ 60 subtracted from the EngineGoverning Torque 58. If split injection is disabled, then PTQ 60 equalsEngine Governing Torque 58, and MTQ 62 equals zero. In one embodiment,PTQ 60 is based on engine RPM, while MTQ 62 and Final Torque 58 arebased on engine RPM and desired torque, leaving MTQ 62 equal to PTQ 60subtracted from Engine Governing Torque 58. PTQ 60, MTQ 62, and FinalTorque 58 are preferably located in look-up tables.

The quantity of fuel to be delivered is represented by the amount ofangular displacement of the crankshaft, preferably measured in degrees,during which a control solenoid of an appropriate injector 14 (FIG. 1)is energized. This signal is referred to as the fuel pulse width.Alternatively, fuel quantity may be represented by a duration of pulseindexed by injection pressure. Two such Pulse Width values aredetermined, subject to further adjustment by other functions such asCylinder Balancing 70 and/or other calibration techniques includinginjector variability compensation based on injector calibration codes.The values of the pulse widths are found in a look-up table referencedby engine operating parameters, such as engine RPM and desired torque.In a preferred embodiment, the desired torque used for this look-upfunction will be either Engine Governing Torque 58 or MTQ 62, and PTQ 60such that two values are obtained.

A Pilot Pulse Width (PPW) 64 corresponds to the value of PTQ 60, while aMain Pulse Width (MPW) 68 corresponds to the value of MTQ 62 or EngineGoverning Torque 58 depending on the system implementation. PPW 64 andMPW 68 may be subsequently subjected to further pulse width adjustmentsuch as SPLIT₋₋ MAIN₋₋ PW₋₋ CORR, in accordance with the presentinvention.

Fuel injector control 72 initiates and terminates the pilot and maininjections, and communicates with logic unit 50 to control fuelinjection. The main injection logic 74, pilot detection delay logic 76,temperature influence adjustment logic 78, and pressure influenceadjustment logic 80 may be applied to PPW 64 and MPW 68. Further, logicunit 50 cooperates with fuel injector control 72 to precisely controlfuel injection timing, as will now be described in detail.

Referring now to FIGS. 3 and 4, a fuel injection timing diagramincluding actuation voltage, solenoid current, control valve position,spray tip needle position and injection rate, and a method forcontrolling fuel delivery are illustrated. When voltage is applied tothe solenoid at the beginning of either the pilot or main pulse, thecontrol valve response includes a rise-time or actuation latency definedas the time duration from voltage application to the control valvereaching the fully actuated position. It is to be appreciated that thepresent invention may be employed in both control valves in which theactuated position is the open position, and in control valves in whichthe actuated position is in the closed position. Further, it is to beunderstood that the term available battery voltage herein means thevoltage that is available to the particular engine component such as aninjector solenoid, and that different components may have differentvoltage levels available for use.

At step 90, a pilot injection rise-time IRT₋₋ PILOT is established. Thisvalue may be established in a variety of different ways. In a preferredembodiment, a filtered injection rise-time is determined based onprevious measured rise-times for the control valve during pilotinjection. IRT₋₋ PILOT may also be established via a static look-uptable, or may be measured in real-time if desired. Typical values forIRT₋₋ PILOT range from about 550 microseconds to about 4500microseconds, and may be contained in a static look-up table populatedby about 17 points, indexed by available battery voltage. At step 92, apilot beginning of injection time BOI₋₋ PILOT is determined based onengine conditions such as engine RPM. When operating in split injectionmode, BOI₋₋ PILOT (split mode) is offset from the BOI₋₋ PILOT (singlemode) to provide adequate time for the pilot injection, inter-pulse gap,and main injections prior to piston top-dead-center to be completed atessentially the same piston position as with single injection.

At step 94, pilot beginning of excitation time BOE₋₋ PILOT isdetermined. BOE₋₋ PILOT precedes BOI₋₋ PILOT by at least the value ofIRT₋₋ PILOT, as best shown in FIG. 3. At step 96, pilot end of injectiontime EOI₋₋ PILOT is determined based on BOI₋₋ PILOT and desired pilotpulse width PPW 64. PPW 64 is based on a desired pilot fuel quantity forpilot injection. At step 98, pilot end of excitation time EOE₋₋ PILOT isdetermined based on the required closing time of the control valve whichis approximated as a constant.

At step 100, a desired inter-pulse gap IPG 66 is determined. Theinter-pulse gap is the crankshaft angle or time interval beginning whenthe control valve reaches the fully unactuated position which terminatespilot injection, and ending when the control valve reaches fullyactuated position at the onset of main injection. IPG 66 is a functionof engine RPM and is preferably not less than IRT₋₋ PILOT. IPG 66 mayalso be based in part on engine torque. In preferred embodiments of thepresent invention, IPG 66 is subjected to a minimum time duration toallow split injection over a wide range of engine RPM. IPG 66 approachesa near constant crankshaft angle as engine RPM decreases, and approachesthe minimum time duration as engine RPM increases. The varying of theinter-pulse gap as described immediately above allows split injectionover an RPM range of, for example, 0 to about 2400 RPM while varying IPG66 between about four and about sixteen degrees of crankshaft angle. Ina preferred embodiment, IPG values populate a look-up table indexed byRPM and having about 17 points. It is to be appreciated that embodimentsof the present invention allow split injection at near any engine speedincluding engine speeds of over 2000 RPM by selecting IRT₋₋ MAIN from aplurality of varying values based on engine conditions.

Main injection rise-time IRT₋₋ MAIN is determined based on IRT₋₋ PILOT,and is preferably adjusted based on inter-pulse gap. Further in apreferred embodiment, IRT₋₋ MAIN is adjusted based on measured availablebattery voltage V₋₋ BAT. Alternatively, IRT₋₋ MAIN may be established inany of the ways described for establishing IRT₋₋ PILOT.

At step 102, rise-time adjustment factors are determined for IRT₋₋ MAIN.As best shown in FIG. 7, IRT₋₋ MULT is found in a look-up table indexedby IPG. As best shown in FIG. 8, IRT₋₋ CORR is found in a look-up tableindexed by V₋₋ BAT. In a preferred embodiment, at step 104, IRT₋₋ MAINis determined according to the following equation:

    IRT.sub.-- MAIN=IRT.sub.-- PILOT*IRT.sub.-- MULT*IRT.sub.--CORR

wherein IRT₋₋ PILOT is the filtered pilot injection rise-time, and IRT₋₋MULT and IRT₋₋ CORR are the main rise-time adjustment factors determinedfrom look-up tables.

In one embodiment, IRT₋₋ MULT ranges from about 0.5 to about 1.16 in alook-up table populated by about 9 points, indexed by engine RPM rangingfrom 0 to about 2400 RPM.

With continuing reference to FIGS. 3 and 4, at step 106, main beginningof excitation time BOE₋₋ MAIN is determined as IRT₋₋ MAIN subtractedfrom the end of the inter-pulse gap IPG 66. It has been found that afterthe control valve reaches the closed position, the control valve retainssome magnetism. This causes faster reaction of the control valve to themain injection excitation than to pilot injection excitation. Thereaction time of the control valve, as affected by retained magnetism,decreases as the inter-pulse gap decreases. To make sure that thecontrol valve reaches the fully unactuated position and has time forvalve bounce to settle prior to main excitation, BOE₋₋ MAIN is subjectto a minimum time according to the following equation:

    BOE.sub.-- MAIN=max (t.sub.CLOSED +EPIGMN, t.sub.CLOSED +IPG-IRT.sub.-- MAIN)

wherein max () is a function which returns the greater of theparenthetical values, t_(CLOSED) is the time at which the control valvefell to its at rest or unactuated position, EPIGMN is a minimum gap timeof preferably at least about 50 microseconds, IPG is the desiredinter-pulse gap, and IRT₋₋ MAIN is the determined main injectionrise-time. The first parenthetical value above represents a minimumexcitation time for the control valve; the second parenthetical valuerepresents a desired excitation time for the control valve.

At step 108, a main end of injection time EOI₋₋ MAIN is determined basedon BOI₋₋ MAIN and desired main pulse width MPW 68. MPW 68 is based on adesired main fuel quantity based on engine conditions. At step 110,pilot end of excitation time EOE₋₋ PILOT is determined based on therequired closing time of the control valve which is approximated as aconstant.

With continuing reference to FIG. 3, in one embodiment of the presentinvention, split injection is enabled based on the value of V_(BAT)according to a hysteresis comparator. The cooperator has upper and lowerthreshold voltages V_(TH) and V_(TL) respectively, which for example areequal to 20 V and 19.2 V, respectively. The lower threshold is a voltagesufficient to allow split injection below which split injection becomesdisabled either for reasons based on the control system hardware, orbecause the rise-time values are unreasonably large. The upper thresholdis that above which disabled split injection is again permitted, whichprevents rapid toggling in and out of split injection mode.

It is to be understood that there may be any number of other conditionsthat must be met in order to allow split injection. One example is thatthe Engine Governing Torque 58 is between predetermined minimum andmaximum torque values. It is to be appreciated that the presentinvention allows split injection at a wide range of engine speeds andloads, and that individual conditions that may enable or disable splitinjection are for further enhancement of engine performance.

Referring now to FIGS. 3 and 5, a method of the present invention fordetermining filtered injection rise-time will be described. At step 120,available battery voltage V₋₋ BAT is measured. At step 122, raw pilotinjection rise-time RAW₋₋ IRT₋₋ PILOT is measured by detecting the pilotinjection opening of the control valve in response to pilot excitationat time IRT₋₋ DETECT. By detecting when the control valve is at thefully actuated position which is indicated by the current inflection orchange in impedance (FIG. 3), control valve rise-time or actuationlatency is measured. At step 124, as best shown in FIG. 9, a pilot valveopening detection delay adjustment factor DETECT₋₋ DELAY is determined.Pressure contour lines are shown to illustrate the varying of DETECT₋₋DELAY with differing common rail injection pressures. In a fuelinjection system that uses unit pumps rather than common rail 16,DETECT₋₋ DELAY may be based on V₋₋ BAT and/or fuel supply pressure andengine RPM. At step 126, an adjusted pilot rise-time IRT₋₋ PILOT isdetermined by subtracting DETECT₋₋ DELAY from RAW₋₋ IRT₋₋ PILOT. At step128, filtered injection rise time is determined. The filter ideallyrejects erroneous IRT₋₋ PILOT values and reduces shot-to-shot variation.

In one embodiment, DETECT₋₋ DELAY ranges from about -30 microseconds toabout 65 microseconds and is indexed by pressures ranging from 0 toabout 2200 Bar, and battery voltages from 0 to about 51 Volts. Thelook-up table as described immediately above is populated by about 150points.

Referring to FIGS. 3 and 6, a method of the present invention fordetermining adjusted pulse width in a common rail embodiment of thepresent invention will now be described. At step 130, actual railpressure for fuel injection is measured. At step 132, a desired railpressure for fuel injection is determined based on engine RPM anddesired engine torque. At step 134, as best shown in FIG. 10, anadjustment factor PW₋₋ CORR is determined from a look-up table indexedby P₋₋ RATIO. P₋₋ RATIO is the ratio of measured rail pressure todesired rail pressure. PPW 64 and MPW 68 are adjusted by multiplying theunadjusted or raw pulse width value by PW₋₋ CORR.

With reference to FIG. 3, additional aspects of the present inventionwill now be described. At decreased available battery voltages, thecontrol valve takes longer to open as shown in dashed lines.Accordingly, the voltage is applied earlier at BOE₋₋ PILOT', causingearlier current ramp up resulting in earlier beginning of control valvemotion. Although the voltage is applied at a time BOI₋₋ PILOT' such thatthe control valve will reach the full open position at the same time aswhen greater voltage is applied at BOI₋₋ PILOT, the earlier lifting ofthe control valve from its seat causes earlier needle lifting. As shown,the injection rate increases sooner after valve full open at decreasedavailable battery voltages. To compensate for this, an injection delayINJECT₋₋ DELAY look-up table indexed by available battery voltage V₋₋BAT is provided, as best shown in FIG. 11.

In one embodiment, INJECT₋₋ DELAY ranges from about 360 to about 410microseconds and is indexed by battery voltages ranging from 0 to 51volts. The look-up table is populated by about 17 points.

Based on the determined value of INJECT₋₋ DELAY which is the delaybetween the control valve reaching the full open position and the startof fuel injection BOI₋₋ PILOT, a compensated BOE₋₋ PILOT will causeBOI₋₋ PILOT to occur when desired, compensating for travel time of thecontrol valve. For example, as shown in FIG. 3, BOE₋₋ PILOT" causesinjection at the desired BOI₋₋ PILOT at the reduced available batteryvoltage shown in dashed lines.

An injection delay INJECT₋₋ DELAY also occurs at main injection as shownin FIG. 3. In a preferred embodiment, this injection delay is alsocompensated for at the main injection, and is additionally adjusted byadjusting the main pulse width MPW 68. An adjustment factor SPLIT₋₋MAIN₋₋ PW₋₋ CORR is determined from look-up table as best shown in FIG.12, indexed by available battery voltage V₋₋ BAT. SPLIT₋₋ MAIN₋₋ PW₋₋CORR is added to the raw main pulse width to produce an adjusted pulsewidth MPW 68. This adjustment is to compensate for the influence uponmain pulse quantity of V₋₋ BAT, hence making possible a smoothtransition between split and single injection without disturbing theengine torque governor, regardless of operating conditions.

In one embodiment, SPLIT₋₋ MAIN₋₋ PW₋₋ CORR ranges from about -160 toabout 140 microseconds, and is located in a look-up table populated byabout 9 points, indexed by battery voltages ranging from about 6 toabout 32 Volts.

It is to be appreciated that the present invention eliminates theproblems associated with main injection valve opening detection,indicated at A (FIG. 3), in which the current inflection may bedifficult to accurately detect and the rise-times may vary due tomagnetism of the control valve from the pilot pulse. By establishingmain rise-time, and by determining main injection initiation controltimes based on the established main rise-time IRT₋₋ MAIN, enhanced splitinjection is possible and practical at a wide range of engine speeds andloads and within a range of battery voltage. Increased valve openingdetection noise which would otherwise cause unacceptable imprecisionwhich grows more intolerable at high engine speeds is avoided by methodsof the present invention which eliminate the need to detect maininjection valve opening, and preferably utilize a filtered injectionrise-time based on the pilot injection measured rise-times.

While the best mode contemplated for carrying out the invention has beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A method of controlling fuel delivery in a fuelinjector having an electronic control valve, the methodcomprising:establishing a pilot injection rise-time for the controlvalve; determining a pilot beginning of excitation time based on thepilot injection rise-time; determining an inter-pulse gap between apilot injection termination and a main injection actuation based onengine conditions; establishing a main injection rise-time for thecontrol valve; determining a main injection beginning of excitation timebased on the desired inter-pulse gap and the main injection rise-time toallow split injection over a wide range of engine speeds; determining anobserved fuel injection pressure; determining a desired fuel injectionpressure based on engine conditions; determining a non-linear pulseadjustment factor based on the measured fuel injection pressure and thedesired fuel injection pressure, the pulse adjustment factor beinggenerally inversely proportional to the observed fuel injectionpressure; determining a fuel quantity based on engine conditions; anddetermining the pulse width based on the fuel quantity and the pulseadjustment factor.
 2. The method of claim 1 wherein determining thepulse adjustment factor further comprises:determining the pulseadjustment factor based on a ratio of the measured fuel injectionpressure to the desired fuel injection pressure.
 3. The method of claim2 wherein the pulse adjustment factor is determined from a look-up tableindexed by the ratio.
 4. The method of claim 1 wherein the fuel quantityis a pilot injection fuel quantity.
 5. The method of claim 1 wherein thefuel quantity is a main injection fuel quantity.
 6. A method ofdetermining a pulse width for an electronic fuel injection in a commonrail system, the method comprising:determining an observed fuelinjection pressure; determining a desired fuel injection pressure basedon engine conditions; determining a non-linear pulse adjustment factorbased on the measured fuel injection pressure and the desired fuelinjection pressure, the pulse adjustment factor being generallyinversely proportional to the observed fuel injection pressure;determining a fuel quantity based on engine conditions; and determiningthe pulse width based on the fuel quantity and the pulse adjustmentfactor.
 7. The method of claim 6 wherein fuel injection is performed assplit injection including a pilot injection and a main injection, andwherein the fuel quantity is a main injection fuel quantity and thepulse width is a main injection pulse width.
 8. The method of claim 6wherein determining the pulse adjustment factor furthercomprises:determining the pulse adjustment factor based on a ratio ofthe measured fuel injection pressure to the desired fuel injectionpressure.
 9. The method of claim 8 wherein the pulse adjustment factoris determined from a look-up table indexed by the ratio.
 10. The methodof claim 6 wherein the fuel quantity is a pilot injection fuel quantity.11. The method of claim 6 wherein the fuel quantity is a main injectionfuel quantity.